/Engine/Plugins/Runtime/MassEntity/Source/MassEntity/Public/MassProcessor.h
RequestedGroupName can indicate a multi-level group name, like so: A.B.C We need to extract the highest-level group name ('A' in the example), and see if it already exists. If not, create it.
[UMassCompositeProcessor](API\Plugins\MassEntity\UMassCompositeProcessor) * FindOrAddGroupProcessor ( [FName](API\Runtime\Core\UObject\FName) RequestedGroupName, [FString](API\Runtime\Core\Containers\FString) * OutRemainingGroupName )